View source for FAQ/Preprocessing

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[[Category:FAQSection]]

== FAQ Section [[faqnumber::5]]: [[faqname::Preprocessing]] ==
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[[faqdescription::Preparing the simulations]]
=== How to quickly change the mesh with blockMesh ===
A description how to achieve this with <tt>m4</tt> can be found here: [[HowTo_blockMesh_with_m4|How to quickly change the mesh with blockMesh]]

=== How do I set up a two-dimensional axisymmetric problem? ===
You use a contributed utility called [http://openfoamwiki.net/index.php/Contrib_MakeAxialMesh makeAxialMesh].

=== How to export a Fluent mesh in ASCII? ===
For more information, read these posts:
* [http://www.cfd-online.com/Forums/ansys-meshing/72929-ansys-fluent-mesh-export-ascii-format.html#post247917 ANSYS Meshing & Geometry - ANSYS to Fluent mesh export in ASCII format post #2]
* [http://www.cfd-online.com/Forums/ansys-meshing/72929-ansys-fluent-mesh-export-ascii-format.html#post295748 ANSYS Meshing & Geometry - ANSYS to Fluent mesh export in ASCII format post #11]
* [http://www.cfd-online.com/Forums/openfoam-meshing-other/61672-fluent3dmeshtofoam-3.html#post360907  OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa - Fluent3DMeshToFoam post #48]
* [http://www.cfd-online.com/Forums/openfoam-meshing-other/74389-fluent-mesh-xp32-openfoam.html  OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa - Fluent Mesh (XP32) to OpenFoam]

=== How to convert Fluent mesh to OpenFOAM? ===
Read these wiki pages:
* [[FluentMeshToFoam]]
* [[Fluent3DMeshToFoam]]
* [[Howto importing fluent mesh with internal walls]]
* [[Import a fluent mesh with interfaces]]

=== Why do I always get the error message "cannot find file" when converting a mesh? ===
For example, you're trying to convert a Fluent mesh to OpenFOAM and you get this error message after you run the conversion utility:
<bash>Create time

--> FOAM FATAL IO ERROR: 
cannot find file

file: /home/ofuser/Desktop/system/controlDict at line 0.

    From function regIOobject::readStream()
    in file db/regIOobject/regIOobjectRead.C at line 73.

FOAM exiting</bash>

Well, the error message should be self-explanatory: it cannot find a file that doesn't exist, namely the file {{tt|system/controlDict}}. This is because OpenFOAM's applications almost always need a configured case folder to work in, so that it can know that it can operate within that folder and what are the settings to be used for doing what you want it to do.

Confused? Please read and study the chapter 2 of the OpenFOAM User Guide, which has 3 tutorials which explain most of the bases of what's needed for using OpenFOAM. Then study the tutorial case {{tt|incompressible/icoFoam/elbow}}, where you will find a fully prepared cases folder and the file {{tt|elbow.msh}} which has the mesh to be converted from Fluent format to OpenFOAM format. The script {{tt|Allrun}} that is present in the parent folder {{tt|incompressible/icoFoam/}} has the steps for running this case, but essentially it sums up to running these commands:
<bash>fluentMeshToFoam elbow.msh
icoFoam
foamMeshToFluent
foamDataToFluent
</bash>
The first one is what you're looking for. Then it runs the solver and then it runs the commands for exporting the mesh and then results to Fluent format.
Faqdescription	Preparing the simulations +
Faqname	Preprocessing +
Faqnumber	5 +